Fluid piping systems often include junctions between devices where the cross-sectional flow area changes abruptly. A ball valve, which provides volumetric control of fluid flow in a piping system, adjoining a circular pipe is an example of this. Often, immediately preceding a ball valve is a venturi meter, which measures flow rate by measuring a pressure drop across the venturi meter.
The abrupt changes in cross-sectional flow area at these junctions create turbulence in the piping system. Generally, turbulence is undesirable in most piping systems because it results in greater pressure drops, noise, and erosion in the piping system. Furthermore, turbulence makes volumetric control of fluid flow in a piping system difficult.
Some prior systems have recognized the desirability of providing particular cross-sectional flow areas immediately preceding certain devices. For example, controlling volumetric flow rate through a ball valve is difficult because of the nature of the ball valve when the ball valve is being closed. The shape of the bore in the ball valve, and the corresponding shape of the fluid entering the ball valve, combine to produce difficult conditions for providing the desired throttling of fluid flow. Therefore, prior systems have utilized washers having particular shapes immediately preceding the ball valve. However, the shape of these washers do not address turbulence that is created due to abrupt changes in cross-sectional flow areas, and in fact, create additional turbulence, noise, and erosion. Another method for aiding volumetric flow control is to either machine the bore of a ball valve into a predetermined shape, or to provide an insert having a predetermined shape in a ball valve, such as that described in U.S. Pat. No. 5,937,890. However, these methods result in the same problems as the washers discussed above. Additionally, these bores and/or inserts may be expensive to manufacture and may result in extra assembly costs.